As urban and suburban areas have become more and more developed and as population centralization in such urban and suburban areas has increased, these areas have become more and more congested and crowded. This concentration and its accompanying congestion has in turn brought increased traffic congestion and more and more crowded streets. Often such streets are lined on each side by relatively tall buildings or similar structures which limit visibility in many directions and often give rise to streets resembling "concrete canyons" which leave motorists driving on such streets with a forward and rearward view and little or no extended field of vision to detect the approach of potential hazards. For non-emergency type motorists, such congestion and limited field of view may be in some measure accommodated by reducing speed and approaching intersections of similarly restricted view streets at smaller speeds and with greater caution. Thus, for non-emergency motorists, these conditions of congested streets and limited vision may result in annoying and often stressful traffic slowdowns and increased travel times, but in general, remain within the motorist's control.
Emergency vehicles, however, are subject to a far different operating criteria due to the urgency which accompanies their travels throughout the congested urban and suburban areas. Under the urgency of the situation arising usually from the need for immediate care and action at some local within the urban or suburban areas, emergency vehicle drivers operate at higher speeds often at risk to themselves and others.
Emergency vehicles employ audible warning devices such as sirens or the like together with batteries of flashing lights to alert motorists to their approach. Motorists are, of course, required by law to pull over the side of the street and stop in order to give the right of way to such emergency vehicles and to avoid the danger of collision. While, flashing lights and audible warning systems have provided some effect, the limitations imposed upon such systems by crowded building structures close to streets have generally limited the effectiveness of flashing lights to vehicles directly within the emergency vehicle's path. Moreover, the development of automobiles with improved sound insulation and the pervasive use of air-conditioning and similar environmental controls within automobiles together with the tendency of motorists to use automotive sound systems providing music and the like while driving, have combined to greatly limit the effectiveness of audible alert devices such as sirens or the like.
Thus, under these conditions, emergency vehicle operators are often faced with the unenviable choice of either slowing down and thereby loosing response time or assuming the risk of collision and operating at high speeds in a high risk manner. In attempting to meet the need for more effective warning systems operating on behalf of emergency vehicles, practitioners in the art have attempted to develop supplemental systems which cooperate with and enhance the effectiveness of the traditional audible and flashing light alert systems. One such system involves the use of radio controlled or optically controlled traffic lights within the city streets. These systems vary somewhat but generally all include a radio energy or optical communication receiver at each intersection which is able to override the traffic light condition and impose stop signals to all traffic. A transmitting unit within the emergency vehicle broadcasts a control signal which is received and processed by the traffic control receives causing traffic to stop at intersections prior to the emergency vehicle approach.
Other systems have attempted to supplement the flashing light and audible alert systems of emergency vehicles with broadcast warnings usually operative in combination with the vehicle's radio.
While these systems may provide some improvement, they generally fail to reliably alert motorists to the impending approach of an emergency vehicle. In addition, such systems have not provided information as to the character of emergency vehicle approaching.
There remains, therefore, a continuing need in the art for evermore improved emergency vehicle alert systems which permit emergency vehicles to operate at high response speeds without unnecessarily endangering other emergency vehicles or non-emergency vehicles within the travel path.